Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion Using C-Scan Ultrasonic Test Aid

Rosihan Ramin1, Heriana2, Bondan Tiara Sofyan3, Mas Ayu Elita Hafizah4

Abstract: Ultrasonic testing (ultrasonic testing) utilizes high-frequency sound waves to detect damage to a material, composite or workpiece. This test is commonly used to inspect materials made of metal or plastic, as long as the material is not absorbent. In its application, ultrasonic testing uses a workpiece vibrating device called a probe. Ultrasonic waves emitted by the probe will vibrate the atoms in the test material or workpiece. The most ideal method for inspecting defects in composites is the immersion method. The size of the immersion tank must be considered as well as possible in order to accommodate the test object of the required size. C-Scan provides data about the location, size, and shape of the defects that occur, besides C-Scan with very high resolution can produce very detailed images. The specimen tested was a laminated composite made of C-glass/epoxy with material properties. The specimen is in the form of a square with a size of 150mmx100mm (referring to ASTM-D7136-12), the test specimen has a thickness of 2.5 mm and is given an impact load with an energy of 11.3 Joules. Stacking sequence of the test specimen, marking and representing the orientation of the fibers in a single layer (layer) of woven composite. After being given an impact load, there is damage in the form of delamination on the plate. plate damage can be detected by back light and numerical simulation.

Keywords: ultrasonic, material and composite

I. Introduction

Composites are a promising new development. Composites have other advantages, such as forming complex shapes and being light and strong. Composites, unfortunately, are extremely vulnerable to impact loads. Low-velocity impact (LVI) is a type of hazardous impact on composites during manufacturing, operation, or routine inspections. Damage caused by LVI is not visible to the naked eye, but it can significantly reduce the composite's strength, particularly its compression strength.

The detection of BVID damage in composites has been the subject of numerous studies. A. Fahr (1992) used an ultrasonic C-scan to inspect several types of damage to the composite in the study. Meanwhile, Byeongjin Park et al. (2014) used ultrasonic scanning lasers to conduct inspection studies on the delamination and debonding of composites. In his research, Park found that the inspection technique using ultrasonic scanning lasers has several advantages: it can be applied to extreme environmental conditions and results in high resolution. In Katunin's (2015) study, various NDI techniques were used to inspect composite damage. PZT sensing, ultrasonic C-scan, thermography, and vibration testing are the NDI techniques used by Katunin. Katunin discovered that ultrasonic C-scan inspection results in more precise damage detection: depth, size, and location, based on his experience with several NDI techniques. As a result, the ultrasonic C-scan damage inspection technique is suitable for use on multi-layer structures such as composites.

The C-Scan presentation is a more advanced version of the A-Scan and B-Scan displays. C-Scan provides information on the location, size, and shape of defects. Typically, the data displayed by the C-Scan is A-Scan data that has been processed. The C-Scan presentation will display the signal in the form of an oscilloscope in the A-Scan presentation with specific colours. C-Scan images with a high resolution can be very detailed. Figure 5 depicts an example of a C-Scan presentation's output. The results of ultrasonic testing on a composite plate subjected to a low-velocity impact (LVI) load are shown in Figure 5.

II. Research Methods

An inspection tool that can display the location, shape, and size of defects caused by LVI in composites is required to avoid potential dangers. As a result, in ultrasonic testing, C-Scan is the most effective type of display for detecting defects. The following are the ultrasonic C-Scan testing methods commonly used for composite structures, based on the coupling mechanics used:

2.1 Immersion Method

This method uses water to replace the couplant as a "connector" between the probe and the test object. The immersion method involves immersing the composite structure in an immersion tank. The transducer is submerged above but not in contact with the test object.

2.2 Squirter Method

Like the immersion method, the squirter method uses water as a couplant. In this method, water is sprayed on the test object as the probe moves during the scanning process. A through transmission mechanism is always used in the squirter method (Matthias SCHWABE et al., 2010).

2.3 Non-Immersion Method (Portable Probe)

The portable probe method is the most traditional of the three options. The couplant in this method is usually in the form of a gel applied to the specimen's surface before the inspection. This method is highly reliant on the operator's expertise, and it cannot detect damage to every ply laminate (only general damage can be seen). Even so, this method has the advantage of being portable so that the test object can be directly tested in the field.

2.4 Comparison

Explain the inspection methods commonly used for composites in points 2.1 - 2.3. Each of the three methods has its own set of benefits and drawbacks

Table 1summarizes and quantifies the advantages and disadvantages of these methods:

Table 1 Comparison of Ultrasonic C-Scan Methods forComposites

Figure 1. C-Scan Presentation Results (E.V. Gonzalez et al., 2010)

C-Scan for composites is typically performed with an automatic scanning system in which a computer controls the probe movement.

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to

The immersion method is the ideal method for inspecting defects in composites, according to the comparison and quantification performed in

Table 1 In order to accommodate the test object of the required size, the immersion tank's size must be carefully considered.

The probe frequency, type, and size are factors to consider when inspecting composites with ultrasonic testing. The frequency of probes is inversely proportional to the presence of a dead zone (the zone where defects cannot be detected). Because the dead zone size can affect the minimum thickness of the test object that can be accurately inspected, highfrequency probes have a smaller dead zone

Because the amount of defects that can be detected is dependent on the size of the probe diameter, the size probe plays an important role. Another essential factor to consider is the probe's type. Is a conventionalprobe or a phasedarrayprobe to be used? Conventional probes are unquestionably less expensive than phased arrays probe. Despite their high cost, phased array probes will provide a much better response through-thickness than conventional probes

2.5 Research ImplementationStages

The research implementation phase is the core of research activities on testing the damage to composite materials caused by explosions. The stages are as follows:

It is necessary to prepare scenarios when validation is carried out during research procedures so that this method can be carried out in real terms for experimental validation. The following preparations must be made:

2.5.1 Prepare specimens with dimensions of 400 x 400 mm

2.5.2 Prepare test equipment for specimens with the expectation that the test area used for testing is 250 x 250 mm

Figure 2. Dead Zone (El Mustapha Ben, 2015)

Figure 3. Test Specimen

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion……

III. Results and Discussion

Not many ultrasonic C-Scan tools are dedicated to detecting defects in composites in Indonesia. PT Dirgantara Indonesia and PT PupukSriwidjaja are two Indonesian companies that own the ultrasonic C-Scan tool. PT Dirgantara Indonesia has been developing composite-material fighter aircraft in recent years. To ensure that the composite structure used is of high quality. This tool uses the squirter method with through transmission mechanism. Detailed images of the C-scan ultrasonic test equipment owned by PT Dirgantara Indonesia are presented in Error! Reference source not found.4.

A conventional probe with a frequency of 5 MHz is used in the TTU device of PT Dirgantara Indonesia. The TTU tool can only detect damage on the surface of the laminate and cannot detect damage in all layers Error! Reference source not found.5depicts the inspection findings of PT Dirgantara Indonesia's TTU equipment.

Error! Reference source not found.depicts damage caused by a blast

Figure 4.Through Transmission Ultrasonic (TTU) owned by PT DI (Handoko and HardinalHadi, 2018)

Figure 5. Defects Detected Using TTU PT DI

load on 12-layer carbon fibre.

As shown in the TTU test results in the image above, fiberglass can withstand blast loads and has no delamination.

The results of the TTU test show that fiberglass material laid up by hand has delamination (loss between fibers) and voids (air voids) in the specimens that have been tested, as shown in the image above. Finally, the blast explosion caused damage to the material, but there was no visible damage after the explosion.

The results of the TTU test show that fiberglass material has delamination (release between fibers) and voids (air voids) that are extremely high, causing the material to be damaged.

Table 2. Damage due to blast on 12 layer carbon fiber

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion……

The TTU test results show that there is carbon material delamination on the lower right, which is caused by the blast pressure from the TNT explosion source with a diameter of 18.8 mm, as shown in the image above.

Ultrasonic C-Scan at 5 MHz with phased array probe. The phased array probe is a cutting-edge technology incorporating multiple crystals into a single probe. The tool's shape is depicted in Error! Reference source not found.6.

They tested composite specimens with BVID (barely visible impact damage) using their C-scan. In addition, this research aims to determine the best inspection method for detecting BVID in composites. Metals have different properties than composite materials. As a result, to properly detect BVID damage in composites, special tools with different specifications are required to detect defects in metal.

Olympus MX2 brand ultrasonic C-Scan. A phased array probe with a frequency of 5 MHz is used in the tool. Error! Reference source not found.7depicts this tool

3.1 Ultrasonic C-Scan

Figure 6. Ultrasonic C-Scan with a phased array probe

3.2 Specifications of Ultrasonic C-Scan tool

Error! Reference source not found.7 shows some of the test equipment commonly used to detect damage to steel components Error! Reference source not found.8shows a standard reference block (SRB) type IIW (international institute of welding) used to calibrate the tool

Error! Reference source not found.8 depicts an SRB made of 1016 steel. The thickness of the SRB is 25 mm, according to the size details shown inError! Reference source not found.9. The test equipment is placed perpendicular to the thickness of steel with a thickness of 25 mm to calibrate the tool detection capability. Different thickness surfaces or materials are required to calibrate the capability of tools at different thicknesses.A polymer-based component of the SRB can be seen inError! Reference source not found.8. The tool's ability to detect a thickness of 50 mm in steel is calibrated using parts made of this polymer.

(a)

(b) Figure 7. C-Scan: (a) Display Unit, (b) Phased Array Probe Angle

Figure 8. SRB Type IIW (Admin, 2019)

Figure 9. Technical Drawing of SRB Type IIW (Admin, 2019)

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion……

3.3 Composite Specimen Specifications

The specimen to be tested is a C-glass/epoxy laminated composite with the material properties listed in Table 3. As shown in Figure 10, the specimen is in the shape of a square with dimensions of 150mmx100mm (as per ASTM-D7136-12).

An impact load of 11.3 Joules is applied to the test specimen, which has a thickness of 2.5 mm. Table 4 shows the stacking sequence of the test specimens. The orientation of the fibers in one layer of woven composite is represented by the markings (+45/-45) and (0/90).

3. Properties of Test Specimens

Figure 10. Specimen for Drop Weight Impact Test (ASTM, 2005)

The plate suffers damage from delamination after being subjected to an impact load. Backlight detection of plate damage is shown inError! Reference source not found.11 Error! Reference source not found.12 depicts the results of numerical simulation based plate damage detection.

Damage to Specimen detected by (a). Impacted Side and (b) Back Side

Table 4. Stacking Sequence of Test Specimens

depicts the results of the inspections conducted with TTU

TTU inspection did not yield good results, as shown in 3. Surface defects caused by resin cracking when the specimen is removed from the baking pan (see red circle in

Figure 12. Total Delamination on Plates Detected by Numerical Simulation (size 30x30 mm)

3.4 Inspection Results with Ultrasonic Test

Figure 13. (a): Inspection Results with TTU, (b): Test Specimen

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion……

3 (b))are visible in the lower-left corner of 3 (a)

The results of the phased array probe inspection were slightly better than TTU. Regrettably, the C-Scan ultrasonic tool is frequently used to detect damage to steel components. The test results from the tool for composite defect detection are still not very accurate because the defects in the composite are located in the tool's dead zone (dead zone explanations see Error! Reference source not found.2). The results of the Ultrasonic C-Scan probe phased array inspection on composite specimens are shown in Figure14.

Figure114 shows that the inspection results on the composite have a significant amount of noise. In contrast to composites, steel tests produce extremely accurate results (see Error! Reference source not found.15).

Surface laying probe

The proprietary Phased Array C-Scan on steel can provide excellent inspection results, particularly in the throughthickness direction, as shown in Error! Reference source not found.15 There are two visible artificial defects (small circle and large circle), which the Phased Array C-Scan tool can detect, and their depth. These findings show that the tool is very good at detecting flaws. The probe frequency, however, is ineffective for detecting defects in composite specimens. Several methods can be used to improve composite accuracy, including using a probe with a frequency lower than 5 MHz or a composite specimen with a thickness greater than 6 mm.

IV. Conclusion

The phased array probe is a product of extremely advanced technology. Using a conventional probe to detect BVID damage to composites is sufficient. However, a portable probe cannot detect damage to the composite in each layer when using a

Figure1.Phased Array C-Scan Inspection Results on Composite Specimens

Figure 15. Results of Phased Array C-Scan Inspection on Steel

Testing of the Structure of Carbon Fiber Reinforce Polymer Composite Panels Due to Blast Explosion……

different inspection technique since the portable probe must make contact with the coupled specimen during the inspection process. In order to avoid dead zones, thicker specimens or devices with a lower frequency are needed. As a result, the through-thickness area that can be inspected is constrained. A specimen with a thickness of at least 6 mm is needed, and the immersion method utilizing a water medium is the optimum way to find the BVID in each composite layer. Between the probe and the specimen, water acts as a "couplant." The through-transmission approach is not advised for BVID detection in composites because this method also cannot show damage to each layer. Inspection can be carried out using the non-contact method with the specimen submerged, allowing for the detection of BVID at each layer. Additionally, only components with specific geometries can be used through-transmission method.

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